/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.mapred;


import java.io.IOException;
import java.util.regex.Pattern;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceAudience.Private;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.RawComparator;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.mapred.lib.HashPartitioner;
import org.apache.hadoop.mapred.lib.IdentityMapper;
import org.apache.hadoop.mapred.lib.IdentityReducer;
import org.apache.hadoop.mapred.lib.KeyFieldBasedComparator;
import org.apache.hadoop.mapred.lib.KeyFieldBasedPartitioner;
import org.apache.hadoop.mapreduce.MRConfig;
import org.apache.hadoop.mapreduce.MRJobConfig;
import org.apache.hadoop.mapreduce.filecache.DistributedCache;
import org.apache.hadoop.mapreduce.util.ConfigUtil;
import org.apache.hadoop.security.Credentials;
import org.apache.hadoop.util.ClassUtil;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.util.Tool;
import org.apache.log4j.Level;

/** 
 * A map/reduce job configuration.
 * 
 * <p><code>JobConf</code> is the primary interface for a user to describe a 
 * map-reduce job to the Hadoop framework for execution. The framework tries to
 * faithfully execute the job as-is described by <code>JobConf</code>, however:
 * <ol>
 *   <li>
 *   Some configuration parameters might have been marked as 
 *   <a href="{@docRoot}/org/apache/hadoop/conf/Configuration.html#FinalParams">
 *   final</a> by administrators and hence cannot be altered.
 *   </li>
 *   <li>
 *   While some job parameters are straight-forward to set 
 *   (e.g. {@link #setNumReduceTasks(int)}), some parameters interact subtly
 *   with the rest of the framework and/or job-configuration and is relatively
 *   more complex for the user to control finely
 *   (e.g. {@link #setNumMapTasks(int)}).
 *   </li>
 * </ol>
 * 
 * <p><code>JobConf</code> typically specifies the {@link Mapper}, combiner 
 * (if any), {@link Partitioner}, {@link Reducer}, {@link InputFormat} and 
 * {@link OutputFormat} implementations to be used etc.
 *
 * <p>Optionally <code>JobConf</code> is used to specify other advanced facets 
 * of the job such as <code>Comparator</code>s to be used, files to be put in  
 * the {@link DistributedCache}, whether or not intermediate and/or job outputs 
 * are to be compressed (and how), debugability via user-provided scripts 
 * ( {@link #setMapDebugScript(String)}/{@link #setReduceDebugScript(String)}),
 * for doing post-processing on task logs, task's stdout, stderr, syslog. 
 * and etc.</p>
 * 
 * <p>Here is an example on how to configure a job via <code>JobConf</code>:</p>
 * <p><blockquote><pre>
 *     // Create a new JobConf
 *     JobConf job = new JobConf(new Configuration(), MyJob.class);
 *     
 *     // Specify various job-specific parameters     
 *     job.setJobName("myjob");
 *     
 *     FileInputFormat.setInputPaths(job, new Path("in"));
 *     FileOutputFormat.setOutputPath(job, new Path("out"));
 *     
 *     job.setMapperClass(MyJob.MyMapper.class);
 *     job.setCombinerClass(MyJob.MyReducer.class);
 *     job.setReducerClass(MyJob.MyReducer.class);
 *     
 *     job.setInputFormat(SequenceFileInputFormat.class);
 *     job.setOutputFormat(SequenceFileOutputFormat.class);
 * </pre></blockquote>
 * 
 * @see JobClient
 * @see ClusterStatus
 * @see Tool
 * @see DistributedCache
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class JobConf extends Configuration {

  private static final Log LOG = LogFactory.getLog(JobConf.class);

  static{
    ConfigUtil.loadResources();
  }

  /**
   * @deprecated Use {@link #MAPREDUCE_JOB_MAP_MEMORY_MB_PROPERTY} and
   * {@link #MAPREDUCE_JOB_REDUCE_MEMORY_MB_PROPERTY}
   */
  @Deprecated
  public static final String MAPRED_TASK_MAXVMEM_PROPERTY =
    "mapred.task.maxvmem";

  /**
   * @deprecated 
   */
  @Deprecated
  public static final String UPPER_LIMIT_ON_TASK_VMEM_PROPERTY =
    "mapred.task.limit.maxvmem";

  /**
   * @deprecated
   */
  @Deprecated
  public static final String MAPRED_TASK_DEFAULT_MAXVMEM_PROPERTY =
    "mapred.task.default.maxvmem";

  /**
   * @deprecated
   */
  @Deprecated
  public static final String MAPRED_TASK_MAXPMEM_PROPERTY =
    "mapred.task.maxpmem";

  /**
   * A value which if set for memory related configuration options,
   * indicates that the options are turned off.
   * Deprecated because it makes no sense in the context of MR2.
   */
  @Deprecated
  public static final long DISABLED_MEMORY_LIMIT = -1L;

  /**
   * Property name for the configuration property mapreduce.cluster.local.dir
   */
  public static final String MAPRED_LOCAL_DIR_PROPERTY = MRConfig.LOCAL_DIR;

  /**
   * Name of the queue to which jobs will be submitted, if no queue
   * name is mentioned.
   */
  public static final String DEFAULT_QUEUE_NAME = "default";

  static final String MAPREDUCE_JOB_MAP_MEMORY_MB_PROPERTY =
      JobContext.MAP_MEMORY_MB;

  static final String MAPREDUCE_JOB_REDUCE_MEMORY_MB_PROPERTY =
    JobContext.REDUCE_MEMORY_MB;

  /**
   * The variable is kept for M/R 1.x applications, while M/R 2.x applications
   * should use {@link #MAPREDUCE_JOB_MAP_MEMORY_MB_PROPERTY}
   */
  @Deprecated
  public static final String MAPRED_JOB_MAP_MEMORY_MB_PROPERTY =
      "mapred.job.map.memory.mb";

  /**
   * The variable is kept for M/R 1.x applications, while M/R 2.x applications
   * should use {@link #MAPREDUCE_JOB_REDUCE_MEMORY_MB_PROPERTY}
   */
  @Deprecated
  public static final String MAPRED_JOB_REDUCE_MEMORY_MB_PROPERTY =
      "mapred.job.reduce.memory.mb";

  /** Pattern for the default unpacking behavior for job jars */
  public static final Pattern UNPACK_JAR_PATTERN_DEFAULT =
    Pattern.compile("(?:classes/|lib/).*");

  /**
   * Configuration key to set the java command line options for the child
   * map and reduce tasks.
   * 
   * Java opts for the task tracker child processes.
   * The following symbol, if present, will be interpolated: @taskid@. 
   * It is replaced by current TaskID. Any other occurrences of '@' will go 
   * unchanged.
   * For example, to enable verbose gc logging to a file named for the taskid in
   * /tmp and to set the heap maximum to be a gigabyte, pass a 'value' of:
   *          -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc
   * 
   * The configuration variable {@link #MAPRED_TASK_ENV} can be used to pass 
   * other environment variables to the child processes.
   * 
   * @deprecated Use {@link #MAPRED_MAP_TASK_JAVA_OPTS} or 
   *                 {@link #MAPRED_REDUCE_TASK_JAVA_OPTS}
   */
  @Deprecated
  public static final String MAPRED_TASK_JAVA_OPTS = "mapred.child.java.opts";
  
  /**
   * Configuration key to set the java command line options for the map tasks.
   * 
   * Java opts for the task tracker child map processes.
   * The following symbol, if present, will be interpolated: @taskid@. 
   * It is replaced by current TaskID. Any other occurrences of '@' will go 
   * unchanged.
   * For example, to enable verbose gc logging to a file named for the taskid in
   * /tmp and to set the heap maximum to be a gigabyte, pass a 'value' of:
   *          -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc
   * 
   * The configuration variable {@link #MAPRED_MAP_TASK_ENV} can be used to pass 
   * other environment variables to the map processes.
   */
  public static final String MAPRED_MAP_TASK_JAVA_OPTS = 
    JobContext.MAP_JAVA_OPTS;
  
  /**
   * Configuration key to set the java command line options for the reduce tasks.
   * 
   * Java opts for the task tracker child reduce processes.
   * The following symbol, if present, will be interpolated: @taskid@. 
   * It is replaced by current TaskID. Any other occurrences of '@' will go 
   * unchanged.
   * For example, to enable verbose gc logging to a file named for the taskid in
   * /tmp and to set the heap maximum to be a gigabyte, pass a 'value' of:
   *          -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc
   * 
   * The configuration variable {@link #MAPRED_REDUCE_TASK_ENV} can be used to 
   * pass process environment variables to the reduce processes.
   */
  public static final String MAPRED_REDUCE_TASK_JAVA_OPTS = 
    JobContext.REDUCE_JAVA_OPTS;
  
  public static final String DEFAULT_MAPRED_TASK_JAVA_OPTS = "-Xmx200m";
  
  /**
   * @deprecated
   * Configuration key to set the maximum virtual memory available to the child
   * map and reduce tasks (in kilo-bytes). This has been deprecated and will no
   * longer have any effect.
   */
  @Deprecated
  public static final String MAPRED_TASK_ULIMIT = "mapred.child.ulimit";

  /**
   * @deprecated
   * Configuration key to set the maximum virtual memory available to the
   * map tasks (in kilo-bytes). This has been deprecated and will no
   * longer have any effect.
   */
  @Deprecated
  public static final String MAPRED_MAP_TASK_ULIMIT = "mapreduce.map.ulimit";
  
  /**
   * @deprecated
   * Configuration key to set the maximum virtual memory available to the
   * reduce tasks (in kilo-bytes). This has been deprecated and will no
   * longer have any effect.
   */
  @Deprecated
  public static final String MAPRED_REDUCE_TASK_ULIMIT =
    "mapreduce.reduce.ulimit";


  /**
   * Configuration key to set the environment of the child map/reduce tasks.
   * 
   * The format of the value is <code>k1=v1,k2=v2</code>. Further it can 
   * reference existing environment variables via <code>$key</code> on
   * Linux or <code>%key%</code> on Windows.
   * 
   * Example:
   * <ul>
   *   <li> A=foo - This will set the env variable A to foo. </li>
   *   <li> B=$X:c This is inherit tasktracker's X env variable on Linux. </li>
   *   <li> B=%X%;c This is inherit tasktracker's X env variable on Windows. </li>
   * </ul>
   * 
   * @deprecated Use {@link #MAPRED_MAP_TASK_ENV} or 
   *                 {@link #MAPRED_REDUCE_TASK_ENV}
   */
  @Deprecated
  public static final String MAPRED_TASK_ENV = "mapred.child.env";

  /**
   * Configuration key to set the environment of the child map tasks.
   * 
   * The format of the value is <code>k1=v1,k2=v2</code>. Further it can
   * reference existing environment variables via <code>$key</code> on
   * Linux or <code>%key%</code> on Windows.
   * 
   * Example:
   * <ul>
   *   <li> A=foo - This will set the env variable A to foo. </li>
   *   <li> B=$X:c This is inherit tasktracker's X env variable on Linux. </li>
   *   <li> B=%X%;c This is inherit tasktracker's X env variable on Windows. </li>
   * </ul>
   */
  public static final String MAPRED_MAP_TASK_ENV = JobContext.MAP_ENV;
  
  /**
   * Configuration key to set the environment of the child reduce tasks.
   * 
   * The format of the value is <code>k1=v1,k2=v2</code>. Further it can 
   * reference existing environment variables via <code>$key</code> on
   * Linux or <code>%key%</code> on Windows.
   * 
   * Example:
   * <ul>
   *   <li> A=foo - This will set the env variable A to foo. </li>
   *   <li> B=$X:c This is inherit tasktracker's X env variable on Linux. </li>
   *   <li> B=%X%;c This is inherit tasktracker's X env variable on Windows. </li>
   * </ul>
   */
  public static final String MAPRED_REDUCE_TASK_ENV = JobContext.REDUCE_ENV;

  private Credentials credentials = new Credentials();
  
  /**
   * Configuration key to set the logging {@link Level} for the map task.
   *
   * The allowed logging levels are:
   * OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE and ALL.
   */
  public static final String MAPRED_MAP_TASK_LOG_LEVEL = 
    JobContext.MAP_LOG_LEVEL;
  
  /**
   * Configuration key to set the logging {@link Level} for the reduce task.
   *
   * The allowed logging levels are:
   * OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE and ALL.
   */
  public static final String MAPRED_REDUCE_TASK_LOG_LEVEL = 
    JobContext.REDUCE_LOG_LEVEL;
  
  /**
   * Default logging level for map/reduce tasks.
   */
  public static final Level DEFAULT_LOG_LEVEL = Level.INFO;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_ID} instead
   */
  @Deprecated
  public static final String WORKFLOW_ID = MRJobConfig.WORKFLOW_ID;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_NAME} instead
   */
  @Deprecated
  public static final String WORKFLOW_NAME = MRJobConfig.WORKFLOW_NAME;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_NODE_NAME} instead
   */
  @Deprecated
  public static final String WORKFLOW_NODE_NAME =
      MRJobConfig.WORKFLOW_NODE_NAME;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_ADJACENCY_PREFIX_STRING} instead
   */
  @Deprecated
  public static final String WORKFLOW_ADJACENCY_PREFIX_STRING =
      MRJobConfig.WORKFLOW_ADJACENCY_PREFIX_STRING;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_ADJACENCY_PREFIX_PATTERN} instead
   */
  @Deprecated
  public static final String WORKFLOW_ADJACENCY_PREFIX_PATTERN =
      MRJobConfig.WORKFLOW_ADJACENCY_PREFIX_PATTERN;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * use {@link MRJobConfig#WORKFLOW_TAGS} instead
   */
  @Deprecated
  public static final String WORKFLOW_TAGS = MRJobConfig.WORKFLOW_TAGS;

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * not use it
   */
  @Deprecated
  public static final String MAPREDUCE_RECOVER_JOB =
      "mapreduce.job.restart.recover";

  /**
   * The variable is kept for M/R 1.x applications, M/R 2.x applications should
   * not use it
   */
  @Deprecated
  public static final boolean DEFAULT_MAPREDUCE_RECOVER_JOB = true;

  /**
   * Construct a map/reduce job configuration.
   */
  public JobConf() {
    checkAndWarnDeprecation();
  }

  /** 
   * Construct a map/reduce job configuration.
   * 
   * @param exampleClass a class whose containing jar is used as the job's jar.
   */
  public JobConf(Class exampleClass) {
    setJarByClass(exampleClass);
    checkAndWarnDeprecation();
  }
  
  /**
   * Construct a map/reduce job configuration.
   * 
   * @param conf a Configuration whose settings will be inherited.
   */
  public JobConf(Configuration conf) {
    super(conf);
    
    if (conf instanceof JobConf) {
      JobConf that = (JobConf)conf;
      credentials = that.credentials;
    }
    
    checkAndWarnDeprecation();
  }


  /** Construct a map/reduce job configuration.
   * 
   * @param conf a Configuration whose settings will be inherited.
   * @param exampleClass a class whose containing jar is used as the job's jar.
   */
  public JobConf(Configuration conf, Class exampleClass) {
    this(conf);
    setJarByClass(exampleClass);
  }


  /** Construct a map/reduce configuration.
   *
   * @param config a Configuration-format XML job description file.
   */
  public JobConf(String config) {
    this(new Path(config));
  }

  /** Construct a map/reduce configuration.
   *
   * @param config a Configuration-format XML job description file.
   */
  public JobConf(Path config) {
    super();
    addResource(config);
    checkAndWarnDeprecation();
  }

  /** A new map/reduce configuration where the behavior of reading from the
   * default resources can be turned off.
   * <p>
   * If the parameter {@code loadDefaults} is false, the new instance
   * will not load resources from the default files.
   *
   * @param loadDefaults specifies whether to load from the default files
   */
  public JobConf(boolean loadDefaults) {
    super(loadDefaults);
    checkAndWarnDeprecation();
  }

  /**
   * Get credentials for the job.
   * @return credentials for the job
   */
  public Credentials getCredentials() {
    return credentials;
  }
  
  @Private
  public void setCredentials(Credentials credentials) {
    this.credentials = credentials;
  }
  
  /**
   * Get the user jar for the map-reduce job.
   * 
   * @return the user jar for the map-reduce job.
   */
  public String getJar() { return get(JobContext.JAR); }
  
  /**
   * Set the user jar for the map-reduce job.
   * 
   * @param jar the user jar for the map-reduce job.
   */
  public void setJar(String jar) { set(JobContext.JAR, jar); }

  /**
   * Get the pattern for jar contents to unpack on the tasktracker
   */
  public Pattern getJarUnpackPattern() {
    return getPattern(JobContext.JAR_UNPACK_PATTERN, UNPACK_JAR_PATTERN_DEFAULT);
  }

  
  /**
   * Set the job's jar file by finding an example class location.
   * 
   * @param cls the example class.
   */
  public void setJarByClass(Class cls) {
    String jar = ClassUtil.findContainingJar(cls);
    if (jar != null) {
      setJar(jar);
    }   
  }

  public String[] getLocalDirs() throws IOException {
    return getTrimmedStrings(MRConfig.LOCAL_DIR);
  }

  /**
   * Use MRAsyncDiskService.moveAndDeleteAllVolumes instead.
   */
  @Deprecated
  public void deleteLocalFiles() throws IOException {
    String[] localDirs = getLocalDirs();
    for (int i = 0; i < localDirs.length; i++) {
      FileSystem.getLocal(this).delete(new Path(localDirs[i]), true);
    }
  }

  public void deleteLocalFiles(String subdir) throws IOException {
    String[] localDirs = getLocalDirs();
    for (int i = 0; i < localDirs.length; i++) {
      FileSystem.getLocal(this).delete(new Path(localDirs[i], subdir), true);
    }
  }

  /** 
   * Constructs a local file name. Files are distributed among configured
   * local directories.
   */
  public Path getLocalPath(String pathString) throws IOException {
    return getLocalPath(MRConfig.LOCAL_DIR, pathString);
  }

  /**
   * Get the reported username for this job.
   * 
   * @return the username
   */
  public String getUser() {
    return get(JobContext.USER_NAME);
  }
  
  /**
   * Set the reported username for this job.
   * 
   * @param user the username for this job.
   */
  public void setUser(String user) {
    set(JobContext.USER_NAME, user);
  }


  
  /**
   * Set whether the framework should keep the intermediate files for 
   * failed tasks.
   * 
   * @param keep <code>true</code> if framework should keep the intermediate files 
   *             for failed tasks, <code>false</code> otherwise.
   * 
   */
  public void setKeepFailedTaskFiles(boolean keep) {
    setBoolean(JobContext.PRESERVE_FAILED_TASK_FILES, keep);
  }
  
  /**
   * Should the temporary files for failed tasks be kept?
   * 
   * @return should the files be kept?
   */
  public boolean getKeepFailedTaskFiles() {
    return getBoolean(JobContext.PRESERVE_FAILED_TASK_FILES, false);
  }
  
  /**
   * Set a regular expression for task names that should be kept. 
   * The regular expression ".*_m_000123_0" would keep the files
   * for the first instance of map 123 that ran.
   * 
   * @param pattern the java.util.regex.Pattern to match against the 
   *        task names.
   */
  public void setKeepTaskFilesPattern(String pattern) {
    set(JobContext.PRESERVE_FILES_PATTERN, pattern);
  }
  
  /**
   * Get the regular expression that is matched against the task names
   * to see if we need to keep the files.
   * 
   * @return the pattern as a string, if it was set, othewise null.
   */
  public String getKeepTaskFilesPattern() {
    return get(JobContext.PRESERVE_FILES_PATTERN);
  }
  
  /**
   * Set the current working directory for the default file system.
   * 
   * @param dir the new current working directory.
   */
  public void setWorkingDirectory(Path dir) {
    dir = new Path(getWorkingDirectory(), dir);
    set(JobContext.WORKING_DIR, dir.toString());
  }
  
  /**
   * Get the current working directory for the default file system.
   * 
   * @return the directory name.
   */
  public Path getWorkingDirectory() {
    String name = get(JobContext.WORKING_DIR);
    if (name != null) {
      return new Path(name);
    } else {
      try {
        Path dir = FileSystem.get(this).getWorkingDirectory();
        set(JobContext.WORKING_DIR, dir.toString());
        return dir;
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
  }
  
  /**
   * Sets the number of tasks that a spawned task JVM should run
   * before it exits
   * @param numTasks the number of tasks to execute; defaults to 1;
   * -1 signifies no limit
   */
  public void setNumTasksToExecutePerJvm(int numTasks) {
    setInt(JobContext.JVM_NUMTASKS_TORUN, numTasks);
  }
  
  /**
   * Get the number of tasks that a spawned JVM should execute
   */
  public int getNumTasksToExecutePerJvm() {
    return getInt(JobContext.JVM_NUMTASKS_TORUN, 1);
  }
  
  /**
   * Get the {@link InputFormat} implementation for the map-reduce job,
   * defaults to {@link TextInputFormat} if not specified explicity.
   * 
   * @return the {@link InputFormat} implementation for the map-reduce job.
   */
  public InputFormat getInputFormat() {
    return ReflectionUtils.newInstance(getClass("mapred.input.format.class",
                                                             TextInputFormat.class,
                                                             InputFormat.class),
                                                    this);
  }
  
  /**
   * Set the {@link InputFormat} implementation for the map-reduce job.
   * 
   * @param theClass the {@link InputFormat} implementation for the map-reduce 
   *                 job.
   */
  public void setInputFormat(Class<? extends InputFormat> theClass) {
    setClass("mapred.input.format.class", theClass, InputFormat.class);
  }
  
  /**
   * Get the {@link OutputFormat} implementation for the map-reduce job,
   * defaults to {@link TextOutputFormat} if not specified explicity.
   * 
   * @return the {@link OutputFormat} implementation for the map-reduce job.
   */
  public OutputFormat getOutputFormat() {
    return ReflectionUtils.newInstance(getClass("mapred.output.format.class",
                                                              TextOutputFormat.class,
                                                              OutputFormat.class),
                                                     this);
  }

  /**
   * Get the {@link OutputCommitter} implementation for the map-reduce job,
   * defaults to {@link FileOutputCommitter} if not specified explicitly.
   * 
   * @return the {@link OutputCommitter} implementation for the map-reduce job.
   */
  public OutputCommitter getOutputCommitter() {
    return (OutputCommitter)ReflectionUtils.newInstance(
      getClass("mapred.output.committer.class", FileOutputCommitter.class,
               OutputCommitter.class), this);
  }

  /**
   * Set the {@link OutputCommitter} implementation for the map-reduce job.
   * 
   * @param theClass the {@link OutputCommitter} implementation for the map-reduce 
   *                 job.
   */
  public void setOutputCommitter(Class<? extends OutputCommitter> theClass) {
    setClass("mapred.output.committer.class", theClass, OutputCommitter.class);
  }
  
  /**
   * Set the {@link OutputFormat} implementation for the map-reduce job.
   * 
   * @param theClass the {@link OutputFormat} implementation for the map-reduce 
   *                 job.
   */
  public void setOutputFormat(Class<? extends OutputFormat> theClass) {
    setClass("mapred.output.format.class", theClass, OutputFormat.class);
  }

  /**
   * Should the map outputs be compressed before transfer?
   * 
   * @param compress should the map outputs be compressed?
   */
  public void setCompressMapOutput(boolean compress) {
    setBoolean(JobContext.MAP_OUTPUT_COMPRESS, compress);
  }
  
  /**
   * Are the outputs of the maps be compressed?
   * 
   * @return <code>true</code> if the outputs of the maps are to be compressed,
   *         <code>false</code> otherwise.
   */
  public boolean getCompressMapOutput() {
    return getBoolean(JobContext.MAP_OUTPUT_COMPRESS, false);
  }

  /**
   * Set the given class as the  {@link CompressionCodec} for the map outputs.
   * 
   * @param codecClass the {@link CompressionCodec} class that will compress  
   *                   the map outputs.
   */
  public void 
  setMapOutputCompressorClass(Class<? extends CompressionCodec> codecClass) {
    setCompressMapOutput(true);
    setClass(JobContext.MAP_OUTPUT_COMPRESS_CODEC, codecClass, 
             CompressionCodec.class);
  }
  
  /**
   * Get the {@link CompressionCodec} for compressing the map outputs.
   * 
   * @param defaultValue the {@link CompressionCodec} to return if not set
   * @return the {@link CompressionCodec} class that should be used to compress the 
   *         map outputs.
   * @throws IllegalArgumentException if the class was specified, but not found
   */
  public Class<? extends CompressionCodec> 
  getMapOutputCompressorClass(Class<? extends CompressionCodec> defaultValue) {
    Class<? extends CompressionCodec> codecClass = defaultValue;
    String name = get(JobContext.MAP_OUTPUT_COMPRESS_CODEC);
    if (name != null) {
      try {
        codecClass = getClassByName(name).asSubclass(CompressionCodec.class);
      } catch (ClassNotFoundException e) {
        throw new IllegalArgumentException("Compression codec " + name + 
                                           " was not found.", e);
      }
    }
    return codecClass;
  }
  
  /**
   * Get the key class for the map output data. If it is not set, use the
   * (final) output key class. This allows the map output key class to be
   * different than the final output key class.
   *  
   * @return the map output key class.
   */
  public Class<?> getMapOutputKeyClass() {
    Class<?> retv = getClass(JobContext.MAP_OUTPUT_KEY_CLASS, null, Object.class);
    if (retv == null) {
      retv = getOutputKeyClass();
    }
    return retv;
  }
  
  /**
   * Set the key class for the map output data. This allows the user to
   * specify the map output key class to be different than the final output
   * value class.
   * 
   * @param theClass the map output key class.
   */
  public void setMapOutputKeyClass(Class<?> theClass) {
    setClass(JobContext.MAP_OUTPUT_KEY_CLASS, theClass, Object.class);
  }
  
  /**
   * Get the value class for the map output data. If it is not set, use the
   * (final) output value class This allows the map output value class to be
   * different than the final output value class.
   *  
   * @return the map output value class.
   */
  public Class<?> getMapOutputValueClass() {
    Class<?> retv = getClass(JobContext.MAP_OUTPUT_VALUE_CLASS, null,
        Object.class);
    if (retv == null) {
      retv = getOutputValueClass();
    }
    return retv;
  }
  
  /**
   * Set the value class for the map output data. This allows the user to
   * specify the map output value class to be different than the final output
   * value class.
   * 
   * @param theClass the map output value class.
   */
  public void setMapOutputValueClass(Class<?> theClass) {
    setClass(JobContext.MAP_OUTPUT_VALUE_CLASS, theClass, Object.class);
  }
  
  /**
   * Get the key class for the job output data.
   * 
   * @return the key class for the job output data.
   */
  public Class<?> getOutputKeyClass() {
    return getClass(JobContext.OUTPUT_KEY_CLASS,
                    LongWritable.class, Object.class);
  }
  
  /**
   * Set the key class for the job output data.
   * 
   * @param theClass the key class for the job output data.
   */
  public void setOutputKeyClass(Class<?> theClass) {
    setClass(JobContext.OUTPUT_KEY_CLASS, theClass, Object.class);
  }

  /**
   * Get the {@link RawComparator} comparator used to compare keys.
   * 
   * @return the {@link RawComparator} comparator used to compare keys.
   */
  public RawComparator getOutputKeyComparator() {
    Class<? extends RawComparator> theClass = getClass(
      JobContext.KEY_COMPARATOR, null, RawComparator.class);
    if (theClass != null)
      return ReflectionUtils.newInstance(theClass, this);
    return WritableComparator.get(getMapOutputKeyClass().asSubclass(WritableComparable.class), this);
  }

  /**
   * Set the {@link RawComparator} comparator used to compare keys.
   * 
   * @param theClass the {@link RawComparator} comparator used to 
   *                 compare keys.
   * @see #setOutputValueGroupingComparator(Class)                 
   */
  public void setOutputKeyComparatorClass(Class<? extends RawComparator> theClass) {
    setClass(JobContext.KEY_COMPARATOR,
             theClass, RawComparator.class);
  }

  /**
   * Set the {@link KeyFieldBasedComparator} options used to compare keys.
   * 
   * @param keySpec the key specification of the form -k pos1[,pos2], where,
   *  pos is of the form f[.c][opts], where f is the number
   *  of the key field to use, and c is the number of the first character from
   *  the beginning of the field. Fields and character posns are numbered 
   *  starting with 1; a character position of zero in pos2 indicates the
   *  field's last character. If '.c' is omitted from pos1, it defaults to 1
   *  (the beginning of the field); if omitted from pos2, it defaults to 0 
   *  (the end of the field). opts are ordering options. The supported options
   *  are:
   *    -n, (Sort numerically)
   *    -r, (Reverse the result of comparison)                 
   */
  public void setKeyFieldComparatorOptions(String keySpec) {
    setOutputKeyComparatorClass(KeyFieldBasedComparator.class);
    set(KeyFieldBasedComparator.COMPARATOR_OPTIONS, keySpec);
  }
  
  /**
   * Get the {@link KeyFieldBasedComparator} options
   */
  public String getKeyFieldComparatorOption() {
    return get(KeyFieldBasedComparator.COMPARATOR_OPTIONS);
  }

  /**
   * Set the {@link KeyFieldBasedPartitioner} options used for 
   * {@link Partitioner}
   * 
   * @param keySpec the key specification of the form -k pos1[,pos2], where,
   *  pos is of the form f[.c][opts], where f is the number
   *  of the key field to use, and c is the number of the first character from
   *  the beginning of the field. Fields and character posns are numbered 
   *  starting with 1; a character position of zero in pos2 indicates the
   *  field's last character. If '.c' is omitted from pos1, it defaults to 1
   *  (the beginning of the field); if omitted from pos2, it defaults to 0 
   *  (the end of the field).
   */
  public void setKeyFieldPartitionerOptions(String keySpec) {
    setPartitionerClass(KeyFieldBasedPartitioner.class);
    set(KeyFieldBasedPartitioner.PARTITIONER_OPTIONS, keySpec);
  }
  
  /**
   * Get the {@link KeyFieldBasedPartitioner} options
   */
  public String getKeyFieldPartitionerOption() {
    return get(KeyFieldBasedPartitioner.PARTITIONER_OPTIONS);
  }

  /**
   * Get the user defined {@link WritableComparable} comparator for
   * grouping keys of inputs to the combiner.
   *
   * @return comparator set by the user for grouping values.
   * @see #setCombinerKeyGroupingComparator(Class) for details.
   */
  public RawComparator getCombinerKeyGroupingComparator() {
    Class<? extends RawComparator> theClass = getClass(
        JobContext.COMBINER_GROUP_COMPARATOR_CLASS, null, RawComparator.class);
    if (theClass == null) {
      return getOutputKeyComparator();
    }

    return ReflectionUtils.newInstance(theClass, this);
  }

  /** 
   * Get the user defined {@link WritableComparable} comparator for 
   * grouping keys of inputs to the reduce.
   * 
   * @return comparator set by the user for grouping values.
   * @see #setOutputValueGroupingComparator(Class) for details.
   */
  public RawComparator getOutputValueGroupingComparator() {
    Class<? extends RawComparator> theClass = getClass(
      JobContext.GROUP_COMPARATOR_CLASS, null, RawComparator.class);
    if (theClass == null) {
      return getOutputKeyComparator();
    }
    
    return ReflectionUtils.newInstance(theClass, this);
  }

  /**
   * Set the user defined {@link RawComparator} comparator for
   * grouping keys in the input to the combiner.
   *
   * <p>This comparator should be provided if the equivalence rules for keys
   * for sorting the intermediates are different from those for grouping keys
   * before each call to
   * {@link Reducer#reduce(Object, java.util.Iterator, OutputCollector, Reporter)}.</p>
   *
   * <p>For key-value pairs (K1,V1) and (K2,V2), the values (V1, V2) are passed
   * in a single call to the reduce function if K1 and K2 compare as equal.</p>
   *
   * <p>Since {@link #setOutputKeyComparatorClass(Class)} can be used to control
   * how keys are sorted, this can be used in conjunction to simulate
   * <i>secondary sort on values</i>.</p>
   *
   * <p><i>Note</i>: This is not a guarantee of the combiner sort being
   * <i>stable</i> in any sense. (In any case, with the order of available
   * map-outputs to the combiner being non-deterministic, it wouldn't make
   * that much sense.)</p>
   *
   * @param theClass the comparator class to be used for grouping keys for the
   * combiner. It should implement <code>RawComparator</code>.
   * @see #setOutputKeyComparatorClass(Class)
   */
  public void setCombinerKeyGroupingComparator(
      Class<? extends RawComparator> theClass) {
    setClass(JobContext.COMBINER_GROUP_COMPARATOR_CLASS,
        theClass, RawComparator.class);
  }

  /** 
   * Set the user defined {@link RawComparator} comparator for 
   * grouping keys in the input to the reduce.
   * 
   * <p>This comparator should be provided if the equivalence rules for keys
   * for sorting the intermediates are different from those for grouping keys
   * before each call to 
   * {@link Reducer#reduce(Object, java.util.Iterator, OutputCollector, Reporter)}.</p>
   *  
   * <p>For key-value pairs (K1,V1) and (K2,V2), the values (V1, V2) are passed
   * in a single call to the reduce function if K1 and K2 compare as equal.</p>
   * 
   * <p>Since {@link #setOutputKeyComparatorClass(Class)} can be used to control 
   * how keys are sorted, this can be used in conjunction to simulate 
   * <i>secondary sort on values</i>.</p>
   *  
   * <p><i>Note</i>: This is not a guarantee of the reduce sort being 
   * <i>stable</i> in any sense. (In any case, with the order of available 
   * map-outputs to the reduce being non-deterministic, it wouldn't make 
   * that much sense.)</p>
   * 
   * @param theClass the comparator class to be used for grouping keys. 
   *                 It should implement <code>RawComparator</code>.
   * @see #setOutputKeyComparatorClass(Class)
   * @see #setCombinerKeyGroupingComparator(Class)
   */
  public void setOutputValueGroupingComparator(
      Class<? extends RawComparator> theClass) {
    setClass(JobContext.GROUP_COMPARATOR_CLASS,
             theClass, RawComparator.class);
  }

  /**
   * Should the framework use the new context-object code for running
   * the mapper?
   * @return true, if the new api should be used
   */
  public boolean getUseNewMapper() {
    return getBoolean("mapred.mapper.new-api", false);
  }
  /**
   * Set whether the framework should use the new api for the mapper.
   * This is the default for jobs submitted with the new Job api.
   * @param flag true, if the new api should be used
   */
  public void setUseNewMapper(boolean flag) {
    setBoolean("mapred.mapper.new-api", flag);
  }

  /**
   * Should the framework use the new context-object code for running
   * the reducer?
   * @return true, if the new api should be used
   */
  public boolean getUseNewReducer() {
    return getBoolean("mapred.reducer.new-api", false);
  }
  /**
   * Set whether the framework should use the new api for the reducer. 
   * This is the default for jobs submitted with the new Job api.
   * @param flag true, if the new api should be used
   */
  public void setUseNewReducer(boolean flag) {
    setBoolean("mapred.reducer.new-api", flag);
  }

  /**
   * Get the value class for job outputs.
   * 
   * @return the value class for job outputs.
   */
  public Class<?> getOutputValueClass() {
    return getClass(JobContext.OUTPUT_VALUE_CLASS, Text.class, Object.class);
  }
  
  /**
   * Set the value class for job outputs.
   * 
   * @param theClass the value class for job outputs.
   */
  public void setOutputValueClass(Class<?> theClass) {
    setClass(JobContext.OUTPUT_VALUE_CLASS, theClass, Object.class);
  }

  /**
   * Get the {@link Mapper} class for the job.
   * 
   * @return the {@link Mapper} class for the job.
   */
  public Class<? extends Mapper> getMapperClass() {
    return getClass("mapred.mapper.class", IdentityMapper.class, Mapper.class);
  }
  
  /**
   * Set the {@link Mapper} class for the job.
   * 
   * @param theClass the {@link Mapper} class for the job.
   */
  public void setMapperClass(Class<? extends Mapper> theClass) {
    setClass("mapred.mapper.class", theClass, Mapper.class);
  }

  /**
   * Get the {@link MapRunnable} class for the job.
   * 
   * @return the {@link MapRunnable} class for the job.
   */
  public Class<? extends MapRunnable> getMapRunnerClass() {
    return getClass("mapred.map.runner.class",
                    MapRunner.class, MapRunnable.class);
  }
  
  /**
   * Expert: Set the {@link MapRunnable} class for the job.
   * 
   * Typically used to exert greater control on {@link Mapper}s.
   * 
   * @param theClass the {@link MapRunnable} class for the job.
   */
  public void setMapRunnerClass(Class<? extends MapRunnable> theClass) {
    setClass("mapred.map.runner.class", theClass, MapRunnable.class);
  }

  /**
   * Get the {@link Partitioner} used to partition {@link Mapper}-outputs 
   * to be sent to the {@link Reducer}s.
   * 
   * @return the {@link Partitioner} used to partition map-outputs.
   */
  public Class<? extends Partitioner> getPartitionerClass() {
    return getClass("mapred.partitioner.class",
                    HashPartitioner.class, Partitioner.class);
  }
  
  /**
   * Set the {@link Partitioner} class used to partition 
   * {@link Mapper}-outputs to be sent to the {@link Reducer}s.
   * 
   * @param theClass the {@link Partitioner} used to partition map-outputs.
   */
  public void setPartitionerClass(Class<? extends Partitioner> theClass) {
    setClass("mapred.partitioner.class", theClass, Partitioner.class);
  }

  /**
   * Get the {@link Reducer} class for the job.
   * 
   * @return the {@link Reducer} class for the job.
   */
  public Class<? extends Reducer> getReducerClass() {
    return getClass("mapred.reducer.class",
                    IdentityReducer.class, Reducer.class);
  }
  
  /**
   * Set the {@link Reducer} class for the job.
   * 
   * @param theClass the {@link Reducer} class for the job.
   */
  public void setReducerClass(Class<? extends Reducer> theClass) {
    setClass("mapred.reducer.class", theClass, Reducer.class);
  }

  /**
   * Get the user-defined <i>combiner</i> class used to combine map-outputs 
   * before being sent to the reducers. Typically the combiner is same as the
   * the {@link Reducer} for the job i.e. {@link #getReducerClass()}.
   * 
   * @return the user-defined combiner class used to combine map-outputs.
   */
  public Class<? extends Reducer> getCombinerClass() {
    return getClass("mapred.combiner.class", null, Reducer.class);
  }

  /**
   * Set the user-defined <i>combiner</i> class used to combine map-outputs 
   * before being sent to the reducers. 
   * 
   * <p>The combiner is an application-specified aggregation operation, which
   * can help cut down the amount of data transferred between the 
   * {@link Mapper} and the {@link Reducer}, leading to better performance.</p>
   * 
   * <p>The framework may invoke the combiner 0, 1, or multiple times, in both
   * the mapper and reducer tasks. In general, the combiner is called as the
   * sort/merge result is written to disk. The combiner must:
   * <ul>
   *   <li> be side-effect free</li>
   *   <li> have the same input and output key types and the same input and 
   *        output value types</li>
   * </ul>
   * 
   * <p>Typically the combiner is same as the <code>Reducer</code> for the  
   * job i.e. {@link #setReducerClass(Class)}.</p>
   * 
   * @param theClass the user-defined combiner class used to combine 
   *                 map-outputs.
   */
  public void setCombinerClass(Class<? extends Reducer> theClass) {
    setClass("mapred.combiner.class", theClass, Reducer.class);
  }
  
  /**
   * Should speculative execution be used for this job? 
   * Defaults to <code>true</code>.
   * 
   * @return <code>true</code> if speculative execution be used for this job,
   *         <code>false</code> otherwise.
   */
  public boolean getSpeculativeExecution() { 
    return (getMapSpeculativeExecution() || getReduceSpeculativeExecution());
  }
  
  /**
   * Turn speculative execution on or off for this job. 
   * 
   * @param speculativeExecution <code>true</code> if speculative execution 
   *                             should be turned on, else <code>false</code>.
   */
  public void setSpeculativeExecution(boolean speculativeExecution) {
    setMapSpeculativeExecution(speculativeExecution);
    setReduceSpeculativeExecution(speculativeExecution);
  }

  /**
   * Should speculative execution be used for this job for map tasks? 
   * Defaults to <code>true</code>.
   * 
   * @return <code>true</code> if speculative execution be 
   *                           used for this job for map tasks,
   *         <code>false</code> otherwise.
   */
  public boolean getMapSpeculativeExecution() { 
    return getBoolean(JobContext.MAP_SPECULATIVE, true);
  }
  
  /**
   * Turn speculative execution on or off for this job for map tasks. 
   * 
   * @param speculativeExecution <code>true</code> if speculative execution 
   *                             should be turned on for map tasks,
   *                             else <code>false</code>.
   */
  public void setMapSpeculativeExecution(boolean speculativeExecution) {
    setBoolean(JobContext.MAP_SPECULATIVE, speculativeExecution);
  }

  /**
   * Should speculative execution be used for this job for reduce tasks? 
   * Defaults to <code>true</code>.
   * 
   * @return <code>true</code> if speculative execution be used 
   *                           for reduce tasks for this job,
   *         <code>false</code> otherwise.
   */
  public boolean getReduceSpeculativeExecution() { 
    return getBoolean(JobContext.REDUCE_SPECULATIVE, true);
  }
  
  /**
   * Turn speculative execution on or off for this job for reduce tasks. 
   * 
   * @param speculativeExecution <code>true</code> if speculative execution 
   *                             should be turned on for reduce tasks,
   *                             else <code>false</code>.
   */
  public void setReduceSpeculativeExecution(boolean speculativeExecution) {
    setBoolean(JobContext.REDUCE_SPECULATIVE, 
               speculativeExecution);
  }

  /**
   * Get configured the number of reduce tasks for this job.
   * Defaults to <code>1</code>.
   * 
   * @return the number of reduce tasks for this job.
   */
  public int getNumMapTasks() { return getInt(JobContext.NUM_MAPS, 1); }
  
  /**
   * Set the number of map tasks for this job.
   * 
   * <p><i>Note</i>: This is only a <i>hint</i> to the framework. The actual 
   * number of spawned map tasks depends on the number of {@link InputSplit}s 
   * generated by the job's {@link InputFormat#getSplits(JobConf, int)}.
   *  
   * A custom {@link InputFormat} is typically used to accurately control 
   * the number of map tasks for the job.</p>
   * 
   * <b id="NoOfMaps">How many maps?</b>
   * 
   * <p>The number of maps is usually driven by the total size of the inputs 
   * i.e. total number of blocks of the input files.</p>
   *  
   * <p>The right level of parallelism for maps seems to be around 10-100 maps 
   * per-node, although it has been set up to 300 or so for very cpu-light map 
   * tasks. Task setup takes awhile, so it is best if the maps take at least a 
   * minute to execute.</p>
   * 
   * <p>The default behavior of file-based {@link InputFormat}s is to split the 
   * input into <i>logical</i> {@link InputSplit}s based on the total size, in 
   * bytes, of input files. However, the {@link FileSystem} blocksize of the 
   * input files is treated as an upper bound for input splits. A lower bound 
   * on the split size can be set via 
   * <a href="{@docRoot}/../mapred-default.html#mapreduce.input.fileinputformat.split.minsize">
   * mapreduce.input.fileinputformat.split.minsize</a>.</p>
   *  
   * <p>Thus, if you expect 10TB of input data and have a blocksize of 128MB, 
   * you'll end up with 82,000 maps, unless {@link #setNumMapTasks(int)} is 
   * used to set it even higher.</p>
   * 
   * @param n the number of map tasks for this job.
   * @see InputFormat#getSplits(JobConf, int)
   * @see FileInputFormat
   * @see FileSystem#getDefaultBlockSize()
   * @see FileStatus#getBlockSize()
   */
  public void setNumMapTasks(int n) { setInt(JobContext.NUM_MAPS, n); }

  /**
   * Get configured the number of reduce tasks for this job. Defaults to 
   * <code>1</code>.
   * 
   * @return the number of reduce tasks for this job.
   */
  public int getNumReduceTasks() { return getInt(JobContext.NUM_REDUCES, 1); }
  
  /**
   * Set the requisite number of reduce tasks for this job.
   * 
   * <b id="NoOfReduces">How many reduces?</b>
   * 
   * <p>The right number of reduces seems to be <code>0.95</code> or 
   * <code>1.75</code> multiplied by (&lt;<i>no. of nodes</i>&gt; * 
   * <a href="{@docRoot}/../mapred-default.html#mapreduce.tasktracker.reduce.tasks.maximum">
   * mapreduce.tasktracker.reduce.tasks.maximum</a>).
   * </p>
   * 
   * <p>With <code>0.95</code> all of the reduces can launch immediately and 
   * start transfering map outputs as the maps finish. With <code>1.75</code> 
   * the faster nodes will finish their first round of reduces and launch a 
   * second wave of reduces doing a much better job of load balancing.</p>
   * 
   * <p>Increasing the number of reduces increases the framework overhead, but 
   * increases load balancing and lowers the cost of failures.</p>
   * 
   * <p>The scaling factors above are slightly less than whole numbers to 
   * reserve a few reduce slots in the framework for speculative-tasks, failures
   * etc.</p> 
   *
   * <b id="ReducerNone">Reducer NONE</b>
   * 
   * <p>It is legal to set the number of reduce-tasks to <code>zero</code>.</p>
   * 
   * <p>In this case the output of the map-tasks directly go to distributed 
   * file-system, to the path set by 
   * {@link FileOutputFormat#setOutputPath(JobConf, Path)}. Also, the 
   * framework doesn't sort the map-outputs before writing it out to HDFS.</p>
   * 
   * @param n the number of reduce tasks for this job.
   */
  public void setNumReduceTasks(int n) { setInt(JobContext.NUM_REDUCES, n); }
  
  /** 
   * Get the configured number of maximum attempts that will be made to run a
   * map task, as specified by the <code>mapreduce.map.maxattempts</code>
   * property. If this property is not already set, the default is 4 attempts.
   *  
   * @return the max number of attempts per map task.
   */
  public int getMaxMapAttempts() {
    return getInt(JobContext.MAP_MAX_ATTEMPTS, 4);
  }
  
  /** 
   * Expert: Set the number of maximum attempts that will be made to run a
   * map task.
   * 
   * @param n the number of attempts per map task.
   */
  public void setMaxMapAttempts(int n) {
    setInt(JobContext.MAP_MAX_ATTEMPTS, n);
  }

  /** 
   * Get the configured number of maximum attempts  that will be made to run a
   * reduce task, as specified by the <code>mapreduce.reduce.maxattempts</code>
   * property. If this property is not already set, the default is 4 attempts.
   * 
   * @return the max number of attempts per reduce task.
   */
  public int getMaxReduceAttempts() {
    return getInt(JobContext.REDUCE_MAX_ATTEMPTS, 4);
  }
  /** 
   * Expert: Set the number of maximum attempts that will be made to run a
   * reduce task.
   * 
   * @param n the number of attempts per reduce task.
   */
  public void setMaxReduceAttempts(int n) {
    setInt(JobContext.REDUCE_MAX_ATTEMPTS, n);
  }
  
  /**
   * Get the user-specified job name. This is only used to identify the 
   * job to the user.
   * 
   * @return the job's name, defaulting to "".
   */
  public String getJobName() {
    return get(JobContext.JOB_NAME, "");
  }
  
  /**
   * Set the user-specified job name.
   * 
   * @param name the job's new name.
   */
  public void setJobName(String name) {
    set(JobContext.JOB_NAME, name);
  }
  
  /**
   * Get the user-specified session identifier. The default is the empty string.
   *
   * The session identifier is used to tag metric data that is reported to some
   * performance metrics system via the org.apache.hadoop.metrics API.  The 
   * session identifier is intended, in particular, for use by Hadoop-On-Demand 
   * (HOD) which allocates a virtual Hadoop cluster dynamically and transiently. 
   * HOD will set the session identifier by modifying the mapred-site.xml file 
   * before starting the cluster.
   *
   * When not running under HOD, this identifer is expected to remain set to 
   * the empty string.
   *
   * @return the session identifier, defaulting to "".
   */
  @Deprecated
  public String getSessionId() {
      return get("session.id", "");
  }
  
  /**
   * Set the user-specified session identifier.  
   *
   * @param sessionId the new session id.
   */
  @Deprecated
  public void setSessionId(String sessionId) {
      set("session.id", sessionId);
  }
    
  /**
   * Set the maximum no. of failures of a given job per tasktracker.
   * If the no. of task failures exceeds <code>noFailures</code>, the 
   * tasktracker is <i>blacklisted</i> for this job. 
   * 
   * @param noFailures maximum no. of failures of a given job per tasktracker.
   */
  public void setMaxTaskFailuresPerTracker(int noFailures) {
    setInt(JobContext.MAX_TASK_FAILURES_PER_TRACKER, noFailures);
  }
  
  /**
   * Expert: Get the maximum no. of failures of a given job per tasktracker.
   * If the no. of task failures exceeds this, the tasktracker is
   * <i>blacklisted</i> for this job. 
   * 
   * @return the maximum no. of failures of a given job per tasktracker.
   */
  public int getMaxTaskFailuresPerTracker() {
    return getInt(JobContext.MAX_TASK_FAILURES_PER_TRACKER, 3);
  }

  /**
   * Get the maximum percentage of map tasks that can fail without 
   * the job being aborted. 
   * 
   * Each map task is executed a minimum of {@link #getMaxMapAttempts()} 
   * attempts before being declared as <i>failed</i>.
   *  
   * Defaults to <code>zero</code>, i.e. <i>any</i> failed map-task results in
   * the job being declared as {@link JobStatus#FAILED}.
   * 
   * @return the maximum percentage of map tasks that can fail without
   *         the job being aborted.
   */
  public int getMaxMapTaskFailuresPercent() {
    return getInt(JobContext.MAP_FAILURES_MAX_PERCENT, 0);
  }

  /**
   * Expert: Set the maximum percentage of map tasks that can fail without the
   * job being aborted. 
   * 
   * Each map task is executed a minimum of {@link #getMaxMapAttempts} attempts 
   * before being declared as <i>failed</i>.
   * 
   * @param percent the maximum percentage of map tasks that can fail without 
   *                the job being aborted.
   */
  public void setMaxMapTaskFailuresPercent(int percent) {
    setInt(JobContext.MAP_FAILURES_MAX_PERCENT, percent);
  }
  
  /**
   * Get the maximum percentage of reduce tasks that can fail without 
   * the job being aborted. 
   * 
   * Each reduce task is executed a minimum of {@link #getMaxReduceAttempts()} 
   * attempts before being declared as <i>failed</i>.
   * 
   * Defaults to <code>zero</code>, i.e. <i>any</i> failed reduce-task results 
   * in the job being declared as {@link JobStatus#FAILED}.
   * 
   * @return the maximum percentage of reduce tasks that can fail without
   *         the job being aborted.
   */
  public int getMaxReduceTaskFailuresPercent() {
    return getInt(JobContext.REDUCE_FAILURES_MAXPERCENT, 0);
  }
  
  /**
   * Set the maximum percentage of reduce tasks that can fail without the job
   * being aborted.
   * 
   * Each reduce task is executed a minimum of {@link #getMaxReduceAttempts()} 
   * attempts before being declared as <i>failed</i>.
   * 
   * @param percent the maximum percentage of reduce tasks that can fail without 
   *                the job being aborted.
   */
  public void setMaxReduceTaskFailuresPercent(int percent) {
    setInt(JobContext.REDUCE_FAILURES_MAXPERCENT, percent);
  }
  
  /**
   * Set {@link JobPriority} for this job.
   * 
   * @param prio the {@link JobPriority} for this job.
   */
  public void setJobPriority(JobPriority prio) {
    set(JobContext.PRIORITY, prio.toString());
  }
  
  /**
   * Get the {@link JobPriority} for this job.
   * 
   * @return the {@link JobPriority} for this job.
   */
  public JobPriority getJobPriority() {
    String prio = get(JobContext.PRIORITY);
    if(prio == null) {
      return JobPriority.NORMAL;
    }
    
    return JobPriority.valueOf(prio);
  }

  /**
   * Set JobSubmitHostName for this job.
   * 
   * @param hostname the JobSubmitHostName for this job.
   */
  void setJobSubmitHostName(String hostname) {
    set(MRJobConfig.JOB_SUBMITHOST, hostname);
  }
  
  /**
   * Get the  JobSubmitHostName for this job.
   * 
   * @return the JobSubmitHostName for this job.
   */
  String getJobSubmitHostName() {
    String hostname = get(MRJobConfig.JOB_SUBMITHOST);
    
    return hostname;
  }

  /**
   * Set JobSubmitHostAddress for this job.
   * 
   * @param hostadd the JobSubmitHostAddress for this job.
   */
  void setJobSubmitHostAddress(String hostadd) {
    set(MRJobConfig.JOB_SUBMITHOSTADDR, hostadd);
  }
  
  /**
   * Get JobSubmitHostAddress for this job.
   * 
   * @return  JobSubmitHostAddress for this job.
   */
  String getJobSubmitHostAddress() {
    String hostadd = get(MRJobConfig.JOB_SUBMITHOSTADDR);
    
    return hostadd;
  }

  /**
   * Get whether the task profiling is enabled.
   * @return true if some tasks will be profiled
   */
  public boolean getProfileEnabled() {
    return getBoolean(JobContext.TASK_PROFILE, false);
  }

  /**
   * Set whether the system should collect profiler information for some of 
   * the tasks in this job? The information is stored in the user log 
   * directory.
   * @param newValue true means it should be gathered
   */
  public void setProfileEnabled(boolean newValue) {
    setBoolean(JobContext.TASK_PROFILE, newValue);
  }

  /**
   * Get the profiler configuration arguments.
   *
   * The default value for this property is
   * "-agentlib:hprof=cpu=samples,heap=sites,force=n,thread=y,verbose=n,file=%s"
   * 
   * @return the parameters to pass to the task child to configure profiling
   */
  public String getProfileParams() {
    return get(JobContext.TASK_PROFILE_PARAMS,
        MRJobConfig.DEFAULT_TASK_PROFILE_PARAMS);
  }

  /**
   * Set the profiler configuration arguments. If the string contains a '%s' it
   * will be replaced with the name of the profiling output file when the task
   * runs.
   *
   * This value is passed to the task child JVM on the command line.
   *
   * @param value the configuration string
   */
  public void setProfileParams(String value) {
    set(JobContext.TASK_PROFILE_PARAMS, value);
  }

  /**
   * Get the range of maps or reduces to profile.
   * @param isMap is the task a map?
   * @return the task ranges
   */
  public IntegerRanges getProfileTaskRange(boolean isMap) {
    return getRange((isMap ? JobContext.NUM_MAP_PROFILES : 
                       JobContext.NUM_REDUCE_PROFILES), "0-2");
  }

  /**
   * Set the ranges of maps or reduces to profile. setProfileEnabled(true) 
   * must also be called.
   * @param newValue a set of integer ranges of the map ids
   */
  public void setProfileTaskRange(boolean isMap, String newValue) {
    // parse the value to make sure it is legal
      new Configuration.IntegerRanges(newValue);
    set((isMap ? JobContext.NUM_MAP_PROFILES : JobContext.NUM_REDUCE_PROFILES), 
          newValue);
  }

  /**
   * Set the debug script to run when the map tasks fail.
   * 
   * <p>The debug script can aid debugging of failed map tasks. The script is 
   * given task's stdout, stderr, syslog, jobconf files as arguments.</p>
   * 
   * <p>The debug command, run on the node where the map failed, is:</p>
   * <p><blockquote><pre>
   * $script $stdout $stderr $syslog $jobconf.
   * </pre></blockquote>
   * 
   * <p> The script file is distributed through {@link DistributedCache} 
   * APIs. The script needs to be symlinked. </p>
   * 
   * <p>Here is an example on how to submit a script 
   * <p><blockquote><pre>
   * job.setMapDebugScript("./myscript");
   * DistributedCache.createSymlink(job);
   * DistributedCache.addCacheFile("/debug/scripts/myscript#myscript");
   * </pre></blockquote>
   * 
   * @param mDbgScript the script name
   */
  public void  setMapDebugScript(String mDbgScript) {
    set(JobContext.MAP_DEBUG_SCRIPT, mDbgScript);
  }
  
  /**
   * Get the map task's debug script.
   * 
   * @return the debug Script for the mapred job for failed map tasks.
   * @see #setMapDebugScript(String)
   */
  public String getMapDebugScript() {
    return get(JobContext.MAP_DEBUG_SCRIPT);
  }
  
  /**
   * Set the debug script to run when the reduce tasks fail.
   * 
   * <p>The debug script can aid debugging of failed reduce tasks. The script
   * is given task's stdout, stderr, syslog, jobconf files as arguments.</p>
   * 
   * <p>The debug command, run on the node where the map failed, is:</p>
   * <p><blockquote><pre>
   * $script $stdout $stderr $syslog $jobconf.
   * </pre></blockquote>
   * 
   * <p> The script file is distributed through {@link DistributedCache} 
   * APIs. The script file needs to be symlinked </p>
   * 
   * <p>Here is an example on how to submit a script 
   * <p><blockquote><pre>
   * job.setReduceDebugScript("./myscript");
   * DistributedCache.createSymlink(job);
   * DistributedCache.addCacheFile("/debug/scripts/myscript#myscript");
   * </pre></blockquote>
   * 
   * @param rDbgScript the script name
   */
  public void  setReduceDebugScript(String rDbgScript) {
    set(JobContext.REDUCE_DEBUG_SCRIPT, rDbgScript);
  }
  
  /**
   * Get the reduce task's debug Script
   * 
   * @return the debug script for the mapred job for failed reduce tasks.
   * @see #setReduceDebugScript(String)
   */
  public String getReduceDebugScript() {
    return get(JobContext.REDUCE_DEBUG_SCRIPT);
  }

  /**
   * Get the uri to be invoked in-order to send a notification after the job 
   * has completed (success/failure). 
   * 
   * @return the job end notification uri, <code>null</code> if it hasn't
   *         been set.
   * @see #setJobEndNotificationURI(String)
   */
  public String getJobEndNotificationURI() {
    return get(JobContext.MR_JOB_END_NOTIFICATION_URL);
  }

  /**
   * Set the uri to be invoked in-order to send a notification after the job
   * has completed (success/failure).
   * 
   * <p>The uri can contain 2 special parameters: <tt>$jobId</tt> and 
   * <tt>$jobStatus</tt>. Those, if present, are replaced by the job's 
   * identifier and completion-status respectively.</p>
   * 
   * <p>This is typically used by application-writers to implement chaining of 
   * Map-Reduce jobs in an <i>asynchronous manner</i>.</p>
   * 
   * @param uri the job end notification uri
   * @see JobStatus
   */
  public void setJobEndNotificationURI(String uri) {
    set(JobContext.MR_JOB_END_NOTIFICATION_URL, uri);
  }

  /**
   * Get job-specific shared directory for use as scratch space
   * 
   * <p>
   * When a job starts, a shared directory is created at location
   * <code>
   * ${mapreduce.cluster.local.dir}/taskTracker/$user/jobcache/$jobid/work/ </code>.
   * This directory is exposed to the users through 
   * <code>mapreduce.job.local.dir </code>.
   * So, the tasks can use this space 
   * as scratch space and share files among them. </p>
   * This value is available as System property also.
   * 
   * @return The localized job specific shared directory
   */
  public String getJobLocalDir() {
    return get(JobContext.JOB_LOCAL_DIR);
  }

  /**
   * Get memory required to run a map task of the job, in MB.
   * 
   * If a value is specified in the configuration, it is returned.
   * Else, it returns {@link JobContext#DEFAULT_MAP_MEMORY_MB}.
   * <p>
   * For backward compatibility, if the job configuration sets the
   * key {@link #MAPRED_TASK_MAXVMEM_PROPERTY} to a value different
   * from {@link #DISABLED_MEMORY_LIMIT}, that value will be used
   * after converting it from bytes to MB.
   * @return memory required to run a map task of the job, in MB,
   */
  public long getMemoryForMapTask() {
    long value = getDeprecatedMemoryValue();
    if (value < 0) {
      return getLong(JobConf.MAPRED_JOB_MAP_MEMORY_MB_PROPERTY,
          JobContext.DEFAULT_MAP_MEMORY_MB);
    }
    return value;
  }

  public void setMemoryForMapTask(long mem) {
    setLong(JobConf.MAPREDUCE_JOB_MAP_MEMORY_MB_PROPERTY, mem);
    // In case that M/R 1.x applications use the old property name
    setLong(JobConf.MAPRED_JOB_MAP_MEMORY_MB_PROPERTY, mem);
  }

  /**
   * Get memory required to run a reduce task of the job, in MB.
   * 
   * If a value is specified in the configuration, it is returned.
   * Else, it returns {@link JobContext#DEFAULT_REDUCE_MEMORY_MB}.
   * <p>
   * For backward compatibility, if the job configuration sets the
   * key {@link #MAPRED_TASK_MAXVMEM_PROPERTY} to a value different
   * from {@link #DISABLED_MEMORY_LIMIT}, that value will be used
   * after converting it from bytes to MB.
   * @return memory required to run a reduce task of the job, in MB.
   */
  public long getMemoryForReduceTask() {
    long value = getDeprecatedMemoryValue();
    if (value < 0) {
      return getLong(JobConf.MAPRED_JOB_REDUCE_MEMORY_MB_PROPERTY,
          JobContext.DEFAULT_REDUCE_MEMORY_MB);
    }
    return value;
  }
  
  // Return the value set to the key MAPRED_TASK_MAXVMEM_PROPERTY,
  // converted into MBs.
  // Returns DISABLED_MEMORY_LIMIT if unset, or set to a negative
  // value.
  private long getDeprecatedMemoryValue() {
    long oldValue = getLong(MAPRED_TASK_MAXVMEM_PROPERTY, 
        DISABLED_MEMORY_LIMIT);
    if (oldValue > 0) {
      oldValue /= (1024*1024);
    }
    return oldValue;
  }

  public void setMemoryForReduceTask(long mem) {
    setLong(JobConf.MAPREDUCE_JOB_REDUCE_MEMORY_MB_PROPERTY, mem);
    // In case that M/R 1.x applications use the old property name
    setLong(JobConf.MAPRED_JOB_REDUCE_MEMORY_MB_PROPERTY, mem);
  }

  /**
   * Return the name of the queue to which this job is submitted.
   * Defaults to 'default'.
   * 
   * @return name of the queue
   */
  public String getQueueName() {
    return get(JobContext.QUEUE_NAME, DEFAULT_QUEUE_NAME);
  }
  
  /**
   * Set the name of the queue to which this job should be submitted.
   * 
   * @param queueName Name of the queue
   */
  public void setQueueName(String queueName) {
    set(JobContext.QUEUE_NAME, queueName);
  }
  
  /**
   * Normalize the negative values in configuration
   * 
   * @param val
   * @return normalized value
   */
  public static long normalizeMemoryConfigValue(long val) {
    if (val < 0) {
      val = DISABLED_MEMORY_LIMIT;
    }
    return val;
  }

  /** 
   * Find a jar that contains a class of the same name, if any.
   * It will return a jar file, even if that is not the first thing
   * on the class path that has a class with the same name.
   * 
   * @param my_class the class to find.
   * @return a jar file that contains the class, or null.
   */
  public static String findContainingJar(Class my_class) {
    return ClassUtil.findContainingJar(my_class);
  }

  /**
   * Get the memory required to run a task of this job, in bytes. See
   * {@link #MAPRED_TASK_MAXVMEM_PROPERTY}
   * <p>
   * This method is deprecated. Now, different memory limits can be
   * set for map and reduce tasks of a job, in MB. 
   * <p>
   * For backward compatibility, if the job configuration sets the
   * key {@link #MAPRED_TASK_MAXVMEM_PROPERTY}, that value is returned. 
   * Otherwise, this method will return the larger of the values returned by 
   * {@link #getMemoryForMapTask()} and {@link #getMemoryForReduceTask()}
   * after converting them into bytes.
   *
   * @return Memory required to run a task of this job, in bytes.
   * @see #setMaxVirtualMemoryForTask(long)
   * @deprecated Use {@link #getMemoryForMapTask()} and
   *             {@link #getMemoryForReduceTask()}
   */
  @Deprecated
  public long getMaxVirtualMemoryForTask() {
    LOG.warn(
      "getMaxVirtualMemoryForTask() is deprecated. " +
      "Instead use getMemoryForMapTask() and getMemoryForReduceTask()");

    long value = getLong(MAPRED_TASK_MAXVMEM_PROPERTY,
        Math.max(getMemoryForMapTask(), getMemoryForReduceTask()) * 1024 * 1024);
    return value;
  }

  /**
   * Set the maximum amount of memory any task of this job can use. See
   * {@link #MAPRED_TASK_MAXVMEM_PROPERTY}
   * <p>
   * mapred.task.maxvmem is split into
   * mapreduce.map.memory.mb
   * and mapreduce.map.memory.mb,mapred
   * each of the new key are set
   * as mapred.task.maxvmem / 1024
   * as new values are in MB
   *
   * @param vmem Maximum amount of virtual memory in bytes any task of this job
   *             can use.
   * @see #getMaxVirtualMemoryForTask()
   * @deprecated
   *  Use {@link #setMemoryForMapTask(long mem)}  and
   *  Use {@link #setMemoryForReduceTask(long mem)}
   */
  @Deprecated
  public void setMaxVirtualMemoryForTask(long vmem) {
    LOG.warn("setMaxVirtualMemoryForTask() is deprecated."+
      "Instead use setMemoryForMapTask() and setMemoryForReduceTask()");
    if (vmem < 0) {
      throw new IllegalArgumentException("Task memory allocation may not be < 0");
    }

    if(get(JobConf.MAPRED_TASK_MAXVMEM_PROPERTY) == null) {
      setMemoryForMapTask(vmem / (1024 * 1024)); //Changing bytes to mb
      setMemoryForReduceTask(vmem / (1024 * 1024));//Changing bytes to mb
    }else{
      this.setLong(JobConf.MAPRED_TASK_MAXVMEM_PROPERTY,vmem);
    }
  }

  /**
   * @deprecated this variable is deprecated and nolonger in use.
   */
  @Deprecated
  public long getMaxPhysicalMemoryForTask() {
    LOG.warn("The API getMaxPhysicalMemoryForTask() is deprecated."
              + " Refer to the APIs getMemoryForMapTask() and"
              + " getMemoryForReduceTask() for details.");
    return -1;
  }

  /*
   * @deprecated this
   */
  @Deprecated
  public void setMaxPhysicalMemoryForTask(long mem) {
    LOG.warn("The API setMaxPhysicalMemoryForTask() is deprecated."
        + " The value set is ignored. Refer to "
        + " setMemoryForMapTask() and setMemoryForReduceTask() for details.");
  }

  static String deprecatedString(String key) {
    return "The variable " + key + " is no longer used.";
  }

  private void checkAndWarnDeprecation() {
    if(get(JobConf.MAPRED_TASK_MAXVMEM_PROPERTY) != null) {
      LOG.warn(JobConf.deprecatedString(JobConf.MAPRED_TASK_MAXVMEM_PROPERTY)
                + " Instead use " + JobConf.MAPREDUCE_JOB_MAP_MEMORY_MB_PROPERTY
                + " and " + JobConf.MAPREDUCE_JOB_REDUCE_MEMORY_MB_PROPERTY);
    }
    if(get(JobConf.MAPRED_TASK_ULIMIT) != null ) {
      LOG.warn(JobConf.deprecatedString(JobConf.MAPRED_TASK_ULIMIT));
    }
    if(get(JobConf.MAPRED_MAP_TASK_ULIMIT) != null ) {
      LOG.warn(JobConf.deprecatedString(JobConf.MAPRED_MAP_TASK_ULIMIT));
    }
    if(get(JobConf.MAPRED_REDUCE_TASK_ULIMIT) != null ) {
      LOG.warn(JobConf.deprecatedString(JobConf.MAPRED_REDUCE_TASK_ULIMIT));
    }
  }
  

  /* For debugging. Dump configurations to system output as XML format. */
  public static void main(String[] args) throws Exception {
    new JobConf(new Configuration()).writeXml(System.out);
  }

}